5770 is a good card, and has performance around that of a GTX 260 (at nearly half the power consumption, mind you). The 5830 exists for ~240, but I have no idea how well it performs or if it has terribly high power consumption versus performance, since it is a heavily binned chip. The 5850 would be ideal, though.

I originally ordered a 5850 but after 3 weeks of it being back ordered I ordered 2 5770's for around the same cost. ($175 per card not including Canadian taxes + shipping) The 5770's OC great for the price! 100% stable @ 1000 Mhz Core and 1400 Mhz Mem, it surpasses the 5850 in terms of performance but doesn't allow to upgrade to much further down, but once Fermi has matured and ATI release their new architecture for the 6-7 series (or what ever) I am sure I will upgrade and by then the 5000 series will be considered "slow".